This section provides background information related to the present disclosure, which is not necessarily prior art.
Because of high fuel costs and government regulations, consumers increasingly require vehicles to be highly fuel-efficient. Hybrid-electric vehicles are considered to be an important system of increasing fuel efficiency. A typical hybrid-electric vehicle is equipped with an exhaust gas recirculation system that includes an engine operating in conjunction with a regenerative braking system to recharge a battery from the hybrid-electric vehicle's kinetic energy when the vehicle decelerates. Recharging the battery by the regenerative braking system increases fuel efficiency by converting kinetic energy to electricity. Therefore, the regenerative braking system increases the battery state of charge without requiring additional fuel and reduces the vehicle's speed without using a conventional brake, which also increases a vehicle's service life.
When the hybrid-electric vehicle decelerates, the regenerative braking system recharges the battery. When decelerating, the vehicle's wheels drive a motor generator so that kinetic energy of the vehicle is converted into electricity to recharge the battery. If the engine is rotated along with the motor generator, an energy recovery amount by the deceleration may be decreased due to an energy loss, in particular a pumping loss caused by a vacuum in the engine. A system that reduced the vacuum in the engine, while maintaining the vehicle's service life and catalyst temperature would thus be desirable.